Information storage technology and the storage capacity available therefrom has been historically limited by a number of factors. A typical prior art Winchester magnetic storage system includes a magnetic head that has a slider element and a magnetic read/write element and is coupled to a rotary actuator magnet and coil assembly by a suspension actuator arm so as to be positioned over the surface of a spinning magnetic disc. In operation, lift forces are generated by aerodynamic interaction between the magnetic head and the spinning magnetic disc. The lift forces are opposed by spring forces applied by the suspension so that a predetermined flying height is hopefully maintained over a full radial stroke of the radial actuator assembly above the surface of the spinning magnetic disc. Such conventional magnetic heads are constrained by the theoretical limit on the ability to closely pack adjacent magnetic bits on the disc surface and still accurately recover and read each bit of information.
To address this problem, much research is being done in the development of magneto-optical (MO) storage technology which provides a higher a real density. During conventional writing of information in MO disc drives, an incident laser beam heats a selected spot of interest on the MO disc to approximately the Curie point. A time varying vertical bias magnetic field is used to define a pattern of "up" or "down" magnetic domains in a recording layer. Subsequently, as the selected spot of interest cools, information is recorded on the MO disc. The size of the magnetic field that is generated provides a lower limit on a maximum data density that may be recorded on the MO disc. Information access in the MO storage system in turn is limited by the size of the optical spot to which an incident laser beam may be focused on the disc surface. Magneto-optical information access requires the use of polarized laser light for reading and writing information on an MO disc. To read information, MO technology makes use of a magneto-optical effect (kerr effect). To detect a modulation of polarization rotation imposed on the linearly polarized incident laser beam by the recorded domain marks in the recording layer. The polarization rotation (representing the information stored at recorded marks or in the edges of the recorded marks) is embodied in a reflection of the linearly polarized laser beam and is converted by optics and electronics for readout.
It is apparent that an important factor in the ability to accurately read and write information from an MO disc, as well as to rapidly access different storage tracks on the MO disc is the design of the flying head, which carries the various components required for accessing magneto-optical information. The need to carry an optical assembly and a magnetic coil on the flying head has made its physical size and mass rather bulky. Therefore, it is somewhat difficult to provide a head which flies at a constant height over the surface of the disc from the outer diameter (OD) to the inner diameter (ID). This is because the slider, which is the primary part of the flying head which controls the flying characteristics, typically includes a pair of side rails which are positioned along its side edges and are disposed about a recessed area. These side rails form a pair of air bearing surfaces. As the disc rotates, the disc drags air under the slider and along the air bearing surfaces in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the side rails, the compression by the air bearing surfaces causes air pressure between the disc and the air bearing surfaces to increase, which creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface. Of course, since the outer radius of the disc is moving faster than the inner radius of the disc, the linear velocity of the air passing beneath the side rails changes substantially as the slider moves from the OD to the ID. Therefore, compensation must be made in the slider air bearing surface design for this change. It has become known in this technology to define a recess or cavity between the side rails. The air passing beneath the slider expands in the cavity, resulting in a decrease in pressure. The pressure in the cavity may become negative (or subambient) in which case the integral of the pressure over the cavity area provides a self loading force on the slider which forces the slider toward the disc surface. This self loading force or suction is a function of the shape and size of the cavity and is intended to counteract the hydrodynamic lifting force developed along the side rails. The interaction between the positive and negative forces on the slider is intended to reduce the flying height sensitivity with respect to disc velocity, and increase air bearing stiffness. For example, the magnitude of the positive pressure developed along the side rail increases with the sliding velocity. However, the magnitude of the self loading force or suction toward the disc surface also increases with sliding velocity, preventing the slider being forced unduly away from the disc.
A related problem is presented by the skew angle of the slider relative to the direction of the air flow. As the disc rotates, it generates wind or air flow, which is approximately parallel to the discs' tangential velocity. The wind in FIG. 1 is represented by arrow 16 and the discs' tangential velocity by an arrow 22. It is apparent that as the slider is moved from the ID to the OD along an arc 18, that the skew angle .phi. between the longitudinal axis 20 of the slider and the direction of the air flow will change. In a magneto-optical drive, because of the optics which are being supported by the slider, it is desirable to maintain the skew angle symmetrical about the center track of the disc surface. It has been common in the prior art to use a non-symmetrical skew angle to compensate at least in part for the change in wind velocity between the inner and outer diameter. However, that approach is less desirable, and this slider design is intended to achieve a constant fly height across the disc from ID to OD with a symmetrical skew angle.